The enhancement of engine performance that can be attained by varying the valve timing and lift as well as the acceleration, velocity and travel time of the intake and exhaust valves in an engine is well known and appreciated in the art. Many engines today employ four valves per cylinder, i.e., 2 intake and two exhaust valves, to improve overall engine performance, especially at medium to high speed. On the other hand, when a four-valve engine is operated at low speed, it may be desirable to deactivate one of the two intake valves to increase the velocity of air entering the combustion cheer, in order to improve swirl. Thus, a valve system should include a valve deactivator that can deactivate one of the two intake valves and then reactivate it again when necessary, to achieve optimum performance.
Further, even with exhaust valves, it is sometimes desirable to have just one exhaust valve operating at low engine speeds. This may reduce the hydraulic power consumed in valve movement and thus reduce the energy loss by only moving one instead of two valves. Therefore, the ability to deactivate one of two intake (or exhaust) valves is a highly desirable feature in a four valve engine.
In a four valve engine with an electrohydraulic valve train that independently controls each valve, valve deactivation can be performed by terminating the signals going to the control means. In four valve engines, however, independently controlling each engine valve with separate hydraulic valve controls is expensive and can require excessive space. Even so, it is still desirable to be able to independently control each engine valve to account for the various engine operating conditions.
To reduce the number of hydraulic valve controls, the pair of intake valves in each cylinder can be coupled together and operated with the same hydraulic valves and controls; as well, the pair of exhaust valves in each cylinder can be similarly coupled together. An object, of the present invention, is to activate each pair of valves with substantially the same lift and timing for most engine operating conditions. But this is not always possible because of slight differences, that arise due to tolerances in manufacturing, between each valve in a pair.
The need, then, arises for an electrohydraulic valvetrain that will work in a four valve engine to ensure substantially identical lift and timing of each pair of valves when necessary, and will also allow one valve from each pair to be either partially or wholly deactivated when certain engine conditions make it desirable to do so while not requiring separate independent controls for each engine valve in the valvetrain.